Printing to a file is broken with Linux content sandboxing enabled

While investigating legacy/trac#23016 (moved) it turned out that the newly enabled content sandboxing prevents from printing to a file not only on particular Linux setups but outright denies it.

The reason for that is https://bugzilla.mozilla.org/show_bug.cgi?id=1309205. We need to backport

https://hg.mozilla.org/mozilla-central/rev/5c25a123203a https://hg.mozilla.org/mozilla-central/rev/2797f193a147 https://hg.mozilla.org/mozilla-central/rev/5b9702d8fe4e

and

https://hg.mozilla.org/mozilla-central/rev/5e7872cb3b5c

to fix that. As a workaround one can set security.sandbox.content.level to 1.